This invention relates to optical communication circuits and, more particularly, to a self-routing optical communication node implemented using Sagnac optical fiber logic gates.
The speed of present-day electronics is limited by the mobility of electrons and holes in a semi-conductor to around five pico seconds (ps). Capacitance and inductance considerations add additional limits. The Sagnac optical fiber logic gate was developed as part of an effort to achieve an optical digital technology which is capable of clock rates much faster than electronics.
In Sagnac gates, while the issues of contrast, cascadability, logical completeness, temperature sensitivity, energy pulse reshaping, and mechanical stability were of initial concern, they have now been overcome. However, the latency exhibited by Sagnac gates has been a "mixed blessing". On one hand, the long latency has enabled Sagnac gates to reduce jitter tolerance. On the other hand, the long latency has complicated the design of combinatoric circuits requiring feedback. Sagnac gates have been used in a variety of circuit applications including, for example, those described in U.S. Pat. Nos. 5,144,375; 5,155,779; and 5,208,705 as well as those described in pending patent applications entitled "Optical Nyquist Rate Multiplexer and Demultiplexer", Ser. No. 07/961,599 filed on Oct. 15, 1992, by Alan Huang; and "Optical Communications System", Ser. No. 07/950,521 filed on Sep. 25, 1992, by Alan Huang and Ser. No. 07/961,606 filed on Oct. 15, 1992, by Alan Huang.
Notwithstanding, the above described design successes, the long latency of the Sagnac gates continue to present problems in circuits requiring the use of feedback or the storing of logic state information.